Thermoplastic tubing has proven to be particularly useful in the automatic analysis of liquid samples. These systems selectively treat and analyze a plurality of liquid samples that are passed through the tubing in seriatim. For example, in U.S. Pat. Nos. 2,797,149 and 3,241,432, a plurality of liquid samples are introduced successfully as a continuously flowing stream into an analysis apparatus, mixed with reagents and analyzed for particular constituents. The successive liquid samples in the flowing stream are separated by at least one air segment of sufficient volume to occlude the conduit along which the stream is directed. Contamination between successive liquid samples and the flowing stream is prevented by the presence of air segments, which function to maintain the successive samples discreet from one another.
Teflon.RTM. fluoropolymer tubing has proved to be particularly useful in these devices by virtue of its highly non-wetted surface properties. When the surface of the tubing is further coated with a fluorocarbon oil, the thin oil film, together with the shear ratios between the film and the tubing wall virtually encapsulate each liquid sample and prevents the sample from ever contacting the wall of the Teflon.RTM. fluoropolymer tubing. This technology is of particular utility in medical testing by virtue of the large number of tests to be performed on a given sample, and the sometimes limited volume of the sample to be analyzed. In the latest generation of those systems, a single microliter of a sample can be mixed with a reagent and analyzed in a discreet test.
To accurately process liquid samples of this size, to maintain the sample encapsulated within the carrier oil, and to provide a constant and ascertainable throughput for given lengths of tubing, the dimensional characteristics of commercially available Teflon.RTM. fluoropolymer tubing must be improved by several orders of magnitude.
In addition, these automatic liquid analysis systems frequently use optical systems in the analysis step which require the tubing to be optically clear with minimum transmittance losses to avoid analysis errors and excessive recalibration each time the tubing is changed.
Commercially available medical grade clear Teflon.RTM. fluoropolymer tubing does not possess the requisite dimensional and optical characteristics necessary for the latest generation of automatic liquid analyzers. For example, 0.5 mm tubing having the diameters of 0.020" ID and 0.034" OD, is customarily supplied with a tolerance of .+-.0.002", and is frequently milky or cloudy having a transmittance, in the visible range, of 75%, even though the material is technically capable of transmittance of 90 to 95%, depending upon the type of Teflon.RTM. fluoropolymer used.
The present invention describes a method and apparatus for treating this Teflon.RTM. fluoropolymer tubing to vastly improve its dimensional tolerances and its optical transmittance.